Imaging system

ABSTRACT

An electrophoretic imaging system utilizing a pair of electrodes and a suspension of electrically photosensitive particles in an insulating carrier liquid is described in which at least one of the electrodes is porous and contains the suspension in the pores. In one embodiment, the electrodes are spaced adjacent each other and the suspension is fed through the porous electrode into the inter-electrode space during photoelectrophoretic image formation.

United States Patent [191 Carreira [111 3,744,896 [451 July 10,1973

[ IMAGING SYSTEM [75] Inventor: Leonard M. Carreira, Webster, NY. [73] Assignee: Xerox Corporation, Rochester, N.Y.

[22] Filed: Sept. 25, 1970 [21] Appl. No.: 75,386

Related U.S. Application Data [62] Division of Ser. No. 690,579, Dec. 14, 1967.

[S2] U.S. Cl 355/3, 96/12, 96/13, 117/37 LE, 355/4, 355/10 [51] Int. Cl. G03g 15/00, 003g 15/10 [58] Field of Search 355/4, 3, 10, 17; 96/1 R, 1.2, 1.3-, 118/637; 117/37 LE [56] References Cited UNITED STATES PATENTS 3,384,565 5/1968 Tulagin et al 204/181 3,425,829 2/ 1969 Cassiers et al. 96/1 3,472,676 10/1969 Cassiers et al. 117/37 LE 3,081,263 3/1963 Metcalfe et al 355/10 X 3,102,045 8/1963 Metcalfe et a] 1 17/37 LE 3,084,043 4/1963 Gundlach 355/10 X OTHER PUBLlCATlONS T. M. Crawford, Developing Electrostatic Charge Pattemsj lBM Bulletin, Vol. 8, No.4, Sept. 1965, 355/10.

Primary Examiner-Robert P. Greiner Attorney-Richard A. Tomlin [5 7] ABSTRACT An electrophoretic imaging system utilizing a pair of electrodes and a suspension of electrically photosensi tive particles in an insulating carrier liquid is described in which at least one of the electrodes is porous and contains the suspension in the pores. In one embodiment, the electrodes are spaced adjacent each other and the suspension is fed through the porous electrode into the inter-electrode space during photoelectrophoretic image formation.

2 Claims, 5 Drawing Figures PAIENIED JUL 1 0 I973 SHEEIlUFZ FIG. I

INVENTOR. LEONARD M. CARREIRA PAIENIED JUL 1 01m SHEEI 2 0F 2 FIG. 2

FIG. 3

FIG. 4

IMAGING SYSTEM This is a division of application Ser. No. 690,579, filed in the United States, Dec. 14, 1967.

BACKGROUND OF THE INVENTION This invention relates in general to imaging systems and, more specifically, to an improved electrophoretic imaging system.

There has been recently developed an electrophoretic imaging system capable of producing color images which utilizes electrically photosensitive particles. This process is described and claimed in copending applications, Ser. Nos. 384,737, now U.S. Pat. No. 3,384,565 384,681 abandoned in favor of CIP Ser. No. 655,023 now U.S. Pat. No. 3,384,566 and 384,680 abandoned in favor of CIP Ser. No. 518,041 now U.S. Pat. No. 3,383,993. In such an imaging system, variously colored light-absorbing particles are suspended in a nonconductive carrier liquid. The suspension is placed between electrodes, subjected to a potential difference and exposed to an image. Typically, one electrode is planar and fixed while the other electrode is movable across the surface of the first electrode with the suspension between the electrodes. As these steps are completed, selective particle migration takes place in image configuration, providing a visible image at one or both of the electrodes. An essential component of the sys- 5 temis the suspended particles which must be electrically photo-sensitive and which apparently undergo a net change in charge polarity upon exposure to activating electromagnetic radiation, through interaction with one of the electrodes. In a mono-chromatic system, particles of a single color are used, producing a single colored image equivalent to conventional black-andwhite photography. In a polychromatic system, the images are produced in natural color because mixtures of particles of two or more different colors which are each sensitive only to light of a specific wavelength or narrow range of wavelengths are used. Particles used in this system must have both intense and pure colors and be highly photosensitive. i

The imaging suspension must before each image forming cycle be coated onto one of the electrodes to form a thin layer of uniform thickness. Generally, a small amount of the suspension is placed on the electrode and a doctor blade is moved across the electrode surface to distribute the suspension uniformly thereacross. While this system is simple and effective on a laboratory scale, it does not lend itself well to a mechanized automatic system. Also, where the electrode upon which the suspension is to be coated is generally cylindrical in configuration, the degree of uniformity in the suspension layer thickness is dependent upon the degree of concentricity of the roller.

Generally, when a color image is formed, a positive image is formed on one of the electrodes while particles not needed to form the image remain on or migrate to the other electrode. After the image is formed, the electrodes must be cleaned and recoated before the next image is formed. The cleaning step necessarily delays the rapid successive imaging operations which would be desirable in an automated system. Also, it would be desirable if the particles not used to form the image could be recycled and used in the formation of succeeding images.

Thus, there is a continuing need for improvements in electrophoretic imaging systems to permit rapid successive imaging operations and to permit simple and economical automation of the system.

'*' SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with this invention by providing an electrophoretic imaging system in which at least one of the imaging electrodes is porous so that the imaging suspension may be introduced through said porous electrode prior to and during electrophoretic imaging.

BRIEF DESCRIPTION OF THE DRAWINGS The various features, advantages and objects of the present invention will become further apparent from the following description and drawings in which:

FIG. I shows a schematic representation of a simple electrophoretic imaging system;

FIG. 2 shows one embodiment of a porous blocking electrode for electrophoretic imaging according to the system of the present invention;

FIG. 3 shows a second embodiment of a porous blocking electrode; H

FIG. 4 shows still another embodiment of the porous blocking electrode; and,

FIG. 5 shows an alternative embodiment in which the injecting electrode is porous.

Referring now to FIG. I, there is seen a transparent electrode generally designated 1, which in this exemplary instance, is made up of a layer of optically transparent glass 2 overcoated with a thin'optically transparent layer 3 of tin oxide, commercially available under the name NESA glass. This electrode will hereafter be referred to as the injecting" electrode. Coated on the surface of injecting electrode 1 is a thin layer 4 of finely divided photosensitive particles dispersed in an insulating liquid carrier. Photosensitive, for the purposes of this application, refers to the properties of a particle which, once attracted to the injecting electrode, will migrate away from it under the. influence of an applied electric field when his exposed to actinic electromagnetic radiation. For a detailed. theoreticalexplanation of the apparent mechanism of operation of the imaging process, see the above menioned copending applications, Ser. Nos. 384,737 now U.S. Pat. No. 3,384,565, 384,681 abandoned in favor of CIP Ser. No. 655,023 now U.S. Pat. No. 3,384,566 and 384,680, abandoned in favor of CIP Ser. No. 518,041 now U.S. Pat. No. 3,383,993, the disclosures of which are incorporated herein by reference. Adjacent to the liquid suspension 4 is a second electrode 5, hereinafter called the blocking electrode" which is connected to one side of the potential source 6 through a switch 7. The opposite side of potential source 6 is connected to the injecting electrode 1 so that when switch 7 is closed, an electric field is applied across the liquid suspension 4 between electrodes l and 5. An image projector made up of a light source 8, a transparency 9, and a lens 10 is provided to expose the dispersion 4 to a light image of the original transparency 9 to be reproduced. Electrode 5 is made in the form of a roller having a conductive central core 1 1 connected to the potential source 6. The core is covered with a layer of a blocking electrode material 12, which may be any suitable insulating material as further discussed below. The particle suspension is exposed to the image to be reproduced while a potential is applied across blocking and injecting electrodes by closing switch 7. Roller 5 is caused to roll across the top surface of injecting electrode 1 with switch 7 closed during the period of image exposure. This light exposure causes exposed pigment particles originally attracted to electrode 1 to migrate through the liquid and adhere to the surface of the blocking electrode, leaving behind a particulate image on the injecting electrode surface which is a duplicate of the original transparency 9. After exposure the relatively volatile carrier liquid evaporates off, leaving behind the particulate image. This particulate image may then be fixed in place as, for example, by placing a lamination over its top surface or by virtue of a dissolved binder material in the carrier liquid such as paraffin wax or other suitable binder that comes out of the solution as the carrier liquid evaporates. In an alternative, the particulate image remaining on the injecting electrode may be transferred to another surface and fixed thereon. This system can produce either monochromatic or polychromatic images depending upon the type and number of pigments suspended in the carrier liquid and the color of light to which this suspension is exposed in the process. In polychromatic imaging, generally a positive subtractive color image conforming to the original is formed on the surface of injecting electrode 1. In monochromatic imaging, generally a positive image is formed on the injecting electrode 1 and a negative image on blocking electrodeS.

Referring now to FIG. 2, there is seen a schematic representation of one embodiment of a blocking electrode suitable for use in this system of this invention. In this instance, blocking electrode 5 is made up of a conductive core 11 with a surface of blocking electrode material 12, which in this embodiment is porous in nature. The imaging suspension 4 is incorporated into the interstices of porous blocking electrode material 12 rather than being coated on the surface of the injecting electrode. This modified blocking electrode 5 then can be used in a system as described with respect to FIG. 1 above. In operation, the blocking electrode having layer 12 filled with the imaging suspension is rolled across a clean conductive injecting electrode while the image to be reproduced is projected onto the injecting electrode surface. As the imaging suspension comes into contact with the injecting electrode, a positive image corresponding to the original is formed on the injecting electrode surface. Since particles not needed to form the image migrate toward the blocking electrode, these particles will remain within the pores of surface layer 12. After a first image is formed, the imaging particle on the surface of the injecting electrode in image configuration are transferred by any conventional method. Then, another image can be formed by merely passing the porous blocking electrode across the injecting electrode again while an image is projected onto the injecting electrode surface. Generally, several images can be formed from one loading of the porous blocking electrode surface 12. Once the suspension in layer 12 is depleted, the layer 12 is merely reloaded and additional images are made. The porous layer 12 may consist of any porous material which is capable of holding a quantity of the imaging suspension. Typically, this may be a woven or felted cloth like material, a brush-like layer having closely spaced bristles or may be an open cell sponge-like layer. A typical sponge-like material which is suitable for use as layer 12 is sold under the trademark Porelon by the Johnsons Wax Company. The porous layer 12 may be loaded with the imaging suspension by any conventional technique. Typicaly, the layer may be immersed in the suspension and air squeezed out of the porous layer so that the air is replaced by the suspension.

FIG. 3 shows an automatically loadable porous blocking electrode member. The blocking electrode shown in FIG. 3 may be substituted for that shown in FIG. 1 with the imaging suspension 4 dispersed throughout the porous blocking electrode surface 12 instead of being coated on the surface of the injecting electrode 1. In the embodiment shown in FIG. 3, the conductive core 11 is in the form of a sleeve which loosely supports the porous blocking electrode layer 12. Blocking electrode layer 12 can rotate around fixed core 11 as the blocking electrode 5 moves across the surface of the injecting electrode 1. Within core 11 is located a suspension supply means 13 which consists simply of an opening through the conductive core sleeve 11 through which additioanl imaging suspension can be supplied. Also within core sleeve 11 is a suction means 14 through which depleted imaging suspension may be withdrawn for reconstitution. Thus, where polychromatic images are being produced, properly balanced imaging suspension can be constantly introv duced through supply means 13 while depleted suspension which may not have the desired color balance after the formation of a polychromatic image is withdrawn at 14. A housing meanslS may be provided to prevent undesired evaporation of the carrier liquid from the surface of blocking electrode layer 12. This automatic system has advantages over that shown in FIG. 2 where polychromatic images are being produced. For example, if a series of images which are predominantly of a single color are produced, the imaging suspension would rapidly become deficient in particles of that color. However, since the embodiment shown in FIG. 3 fresh imaging suspension is constantly being added, images of uniform color characteristics would be produced.

Referring now to FIG. 4, there is seen a blocking electrode configuration which operates in a manner somewhat similar to that shown in FIG. 3. Conductive core 11 is perforated by openings 16 which connect a hollow center 17 to a thin layer of porous material 18. Thus, imaging suspension introduced into hollow center 17 can be supplied to porous layer 18. A belt of porous or sponge-like material 19 is entrained in contact with the surface of layer 18 and rollers 20 and 21. Layer 19 will thus be filled with the imaging suspension. Roller 20 is fixed in non-rotatable manner and has a suction means 23 opening through a grill like surface against layer 19. Thus, imaging suspension in layer 19 may be removed by means of suction means 23. Proper color balance in the imaging suspension may therefore be maintained since new suspension is constantly being added through layer 18 while spent or depleted suspension is being removed by suction means 23 for reconstitution.

FIG. 5 shows an alternative embodiment in which the conductive injecting electrode is porous and is in roller configuration while the blocking electrode is planar. The arrangement here is in general similar to that shown in FIG. 1 with the blocking and injecting electrodes reversed. A power supply 6 is connected through a switch 7 to the center of conducting injecting electrode 5 and the conductive backing member for blocking electrode 1. The conductive backing member in this instance consists of a glass plate 24 having a thin film of transparent conductive tin oxide 25 on its surface. Over the conductive layer 25 is positioned a layer of blocking electrode material 12 which in this instance is transparent and may consist of any suitable transparent insulating material. The injecting electrode consists of roller having a porous conductive surface. Typically, the surface may be sintered metal or a porous conductive glass. The porous surface of injecting electrode 1 may be loaded by dipping the electrode in a suspension of imaging particles or by introducing the imaging particles to the porous layer from the interior of the roller in a manner similar to that shown in FIGS. 3 and 4. Since in general the positive polychromatic images are formed on the injecting electrode, this embodiment is primarily useful for preparing negative images of monochromatic originals. 1n monochromatic imaging," particles of a single color are used with the positive image ordinarily being formed on the injecting electrode and the negative being formed on the blocking electrode. Therefore, in this embodiment those particles which would form a positive image remain in the porous surface of injecting electrode 1 while a negative image is produced on blocking electrode 12. This embodiment is especially suitable for producing copies which are to be viewed by transmission from negative black-and-white originals. Since blocking electrode layer 12 can easily be replaced between imaging cycles, transfer of the image from the electrode to a receiving sheet is not necessary since the image can be fixed directly to layer 12 and a new sheet of blocking material be used for the next image.

The roller blocking electrode configuration shown in the drawings is, of course, merely representative and any other suitable configuration may be used. Typically, the blocking electrode could be in the form of a movable or stationary flat plate, or in the form of a belt entrained over rollers. The blocking electrode surface may comprise any suitable material having a volume resistivity of at least ohm-centimeters. Where the resistivity of the blocking electrode material is lower than 10' ohm-centimeters, there is a tendency for unwanted pigments which should migrate to the blocking electrode surface and adhere thereto to be reflected back towards the injecting electrode thereby degrading image quality. For highest image quality, it is preferred that the blocking electrode have a volume resistivity of at least l0" ohm-centimeters. 1n the range of 10" to 10" ohm-centimeters the surface charge which develops on the surface of the blocking electrode during imaging can be eliminated merely by a suitable delay between imaging operations to permit surface charge to.

leak off. However, it is preferred that a means be provided for eliminating the undesired surface charge since in high speed automatic imaging equipment it is desirable to produce successive images rapidly without the delay necessary to allow the surface charge to leak off. Where the volume resistivity of the blocking electrode material is greater than 10 ohm-centimeters the time necessary for dissipation of the surface charge is great enough to require external means for removing said charge. One may select from a very great number of possible blocking materials when external means is provided to remove unwanted charge after imaging. As stated above, any suitable material having the desired resistivity may be used. Typical materials include vinyl polymers; polyolefms such as polyethylene, polypropylene, polyisobutylene; polyaromatics such as polystyrene, polyalkyds, polyvinyl toluene, polyphenylene oxides, polysulfone, polyxylenes; polyacrylics and their esters; polyhalocarbons such as vinyl and vinylidene chlorides and fluorides; polyperfluorinated halocarbons such as polytetrafluoroethylene; polyvinyl ethers; polyvinyl acetates; polyvinyl acetals and ketals such as polyvinyl butral; phenolic resins; polyesters; polyethers; silicone resins; polycarbonates; epoxy resins; polyamides; polyimides; urethane resins; polysulfides and copolymers and mixtures thereof.

The blocking electrode material may include dopants or additives to modify resistivity or other physical properties for particular uses. For example, resistivity may be mofified by the addition of carbon black, conductive pigments and dyes, powdered metals, inorganic salts, etc.

Any suitable insulating liquid may be used as the carrier for the pigment particles in the system. Typical carrier liquids include decane, dodecane, N-tetradecane, paraffin, beeswax or other thermoplastic materials, Sohio Odorless Solvent 3440 (a kerosene fraction available from the Standard Oil Company of Ohio), lsopar-G (a long chain saturated aliphatic hydrocarbon available from Humble Oil Company of New Jersey) and mixtures thereof..Good quality images have been produced with voltages ranging from about 300 to about 5,000 volts with either a negative or positive polarity on the blocking electrode core.

Any suitable photosensitive particle or mixtures of such particles may be used in carrying out the imaging process, regardless of whether the particular particle selected is organic, inorganic and is made up of one or more components in solid solution or dispersed one in the other or whether the particles are made up of multiple layers of different materials. Typical photosensitive particles include organics such as 8,13- dioxodinaphtho-(2,l-b;2',3'-d)-furan-6-carbox-pmethoxyanilide; bocarno Red, C. 1. No. 15865, 1-(4- methyl-5'-chloroazobenzene-2-sulfonic acid)-2- hydroxy-3-naphthoic acid; Watchung Red B, the barium salt of l-(4!-methyl-5'-chloroazobenzene-2'- sulfonic acid )-2-hydroxy-3-naphthoic acid, C. 1. No. 15865; Naphthol Red B, l-(2-methoxy-5'- nitrophenylazo)-2-hydroxy-3 '-nitro-3-naphthanilide, C. I. No. 12355; Duol Carmine, the calcium lake of l- (4-methy1azobenzene-2'-su1fonic acid)-2-hydroxy-3- naphthoic acid, C. 1. No. 15850; Calcium Lithol Red,

the calcium lake of l-(2'-azonaphthalene-l'-sulfonic acid)-2-naphthol, C. 1. No.- 15630; Quinacridone and substituted quinacridones such as 2,9-dimethylquina cridone; Pyranthrones; lndofast Brilliant Scarlet Toner, 3 ,4 ,9, l 0-bis(N,N-( p-methoxyphenyl)-imido perylene, C. 1. No. 71140; dichlorothioindigo; Pyrazolone Red B Toner, C. I. No. 21 phthalocyanines including substituted and unsubstituted metal and metalfree phthalocyanines such as copper phthalocyan'me, magnesium phthalocyanine, metal-free phthalocyanine, polychloro substituted phthalocyanines etc.; Methyl Violet, a phosphotungstomolybdic acid lake of a Triphenylmethane dye, C. I. No. 42535; Indofast Violet Lake, dichloro-9,18-isoviolanthrone, C. I. No. 60010; Diane Blue, 3 ,3 -methoxy-4,4"diphenyl-bis( l "-azo-2' '-hydroxy- 3"-naphthanilide, C. I. No. 21180, Indanthrene Brilliant Orange R.K., 4,l-dibromo-6,l2-anthanthrone, C. I. No. 59300; Algol Yellow G.C., l,2,5,6-di(C,C'- diphenyl)-thiazole-anthraquinone, C. I. No. 67300; Flavanthrone; Indofast Orange Toner, C. I. No. 71 105; l-cyano-2,3-phthaloyl-7,8-benzopyrrocoline and many other thioindigos, acetoacetic arylides, anthraquinones, perionones, perylenes, dioxazines, quinacridones, azos, diazos, thoazines, azines and the like; inorganics such as cadmium sulfide, cadmium sulfoselenide, zinc oxide, zinc sulfide, sulphur selenium, mercuric sulfide, lead oxide, lead sulfide, cadmium selenide titanium dioxide, indium trioxide, and the like. In addition to the aforementioned pigments, other organic materials which may be employed in the particles include polyvinylcarbazole; 2,4-bis(4,4'-diethyl-aminophenyl)- 1,3,4-oxidiazole; N-isopropylcarbazole; polyvinylanthracene; triphenylpyrrol; 4,5-diphenylimidazolidinone; 4,5-diphenylimidazolidinone; 4,5- diphenylimidazolidinethione; 4,5-bis-(4'-aminophenyl )-imidazolidinone; 1,2,5 ,6-tetraazacyclooctatetraene-(2,4,6,8); 3,4-di-(4'-methoxyphenyl)-7,8- diphenyl- I ,2,5,6-tetraaza-cyclooctatetraene-( 2,4,6,8 3 ,4-di )4 -phenoxy-phenyl)-7,8-diphenyl-1,2,5 ,6- tetraaza-cyclooctatetraene-(2,4,6,8); 3,4,7,8- tetramethoxyl ,2,5 ,6-tetraazacyclooctatetraene- (2,4,6,8); Z-mercapto-benzthiazole; 2-phenyl-4-alphanuphthylidene-oxazolone; 2-phenyl-4-diphenylideneoxazolone; 2-phenyl-4-p-methoxybenzylideneoxazolone; 6-hydroxy-2-phenyl (p-dimethyLamino phenyl)- benzofurane; 6-hydroxy-2,3-di(p methoxyphenyl)- benzofurane; 2,3 ,5 ,6-tetra-(p-methoxyphenyl)-furo- (3,2f)-benzofurane; 4-dimethylaminobenzylidenebenzhydrazide; 4-dimethylaminobenzylideneisonicotinic acid hydrazide; turfurylidene-(2)-4'-dimethylamino-benzhydrazide; benzilidene-amino-acenaphthene-3-benzylideneamino-carbazole; (4-N,N-dimethylaminobenzylidene)- p-N,N-dimethylaminoaniline; (2-nitro-benzylidene)-pbromo-aniline; N,N-dimethyI-N'-(2-nitro-4-cyanobenzylidene)-p-bromo-aniline; N,N-dimethyl-N'-(2- nitro-4-cyano-benzylidene )-p-phenylene-diamine; 2,4- diphenyl-quinazoline; 2-(4' -amino-phenyl)-4-phenyl-quinazoline; 2-phenyl-4(4'- di-methyl-amino-phenyl)-7-methoxy-quinazoline; 1,3- diphenyl-tetrahydroimidazole; l ,3-di(4 '-chlorophenyl)-tetra-hydroimidazole; l ,3-diphenyl-2,4'- dimethyl aminophenyl)-tetra-hydroimidazole; 1,3- di(p-tolyl)-2-[quinolyl-(2'-)]-tetrahydromimidazole; 3-(4'-di-methylamino-phenyl)-5-(4"-methoxyphenyl)-6-phenyl- I ,2,4-triazine; 3-pyridil-(4")-5-(4- dimethylaminophenyl)-6-phenyl-1,2,4-triazine; 3-(4'- amino-phenyl )-5,6-di-phenyll ,2,4-triazine; 2,5 -bis [4- -amino-phenyl-( l ')]-l,3,3,-triazole; 2,5-bis [4-(N- ethyl-N-acetyl-amino)-phenyl-( l )1 -l ,3,4-triazole; 1,- 5-diphenyl-3-methyl-pyrazoline; l ,3 ,4,5-tetraphenylpyrazoline; I-phenyI-B-(p-methoxy styrl)-5-(pmcthoxy-phenyl )-pyrazoline; l-methyl-2-( 3 ',4 dihydroxy-methylene-phenyl)-benzimidazole; 2-(4'- 8 dimethylamino phenyl)-benzoxazole; 2-(4'-methoxyphenyl)-benzthiazole; 2,5-bis [p-amino-phenyl-(l)]- l,3,4,-oxidiazole; 4,5-diphenyl-imidazolone; 3-aminocarbazole; copolymers and mixtures thereof.

Other materials include organic donor-acceptor (Lewis acid-Lewis base) charge transfer complexes made up of donors such as phenolaldehyde resins, phenoxies, epoxies, polycarbonates, urethanes, styrene or the like complexed with electron acceptors such as 2,4,7-trinitro-9-fluorenone; 2,4,5,7-tetranitro-9- fluorenone; picric acid; 1,3,5-trinitro benzene; chloranil; 2,5-dichloro-benzoquinone; anthraquinone-Z- carboxylic acid, Bromal, 4-nitro-phenol; maleic anhydride; metal halides of the metals and metalloids of groups 1-8 and NIH of the periodic table including, for example, aluminum chloride, zinc chloride, ferric chloride, magnesium chloride, calcium iodide, strontium bromide, chromic bromide, arsenic triiodide, magnesium bromide, stannous chloride etc., boron halides, such as boron trifluorides; ketones such as benzophenone and anisil, mineral acids such as sulfuric acid; organic carboxylic acids such as acetic acid and maleic acid, succinic acid, citroconic acid, sulphonic acid, such as 4-toluene sulphonic acid and mixtures thereof. In addition to the charge transfer complexes, it is to be noted that many additional ones of the above materials may be further sensitized by the charge transfer complexing technique and that many of these materials may be dye-sensitized to narrow, broaden or heighten their spectral response curves.

As stated above, any suitable particle structure may be employed. Typical particles include those which are made up of only the pure photosensitive material or a sensitized form thereof, solid solutions or dispersions of the photosensitive material in a matrix such as thermoplastic or thermosetting resins, copolymers of photosensitive pigments and organic monomers, multilayers of particles in which the photosensitive material is included in one of the layers and where other layers provide light filtering action in an outer layer or a fusible or solvent softenable core of resin or a core of liquid such as dye or other marking material or a core of one photosensitive material coated with an overlayer of another photosensitive material to achieve broadened spectral response. Other photo-sensitive structures include solutions, dispersions, or copolymers of one photosensitive material in another with or without other photosensitively inert materials. Other particle structures which may be used but which are not required include those described in U. S. Pat. No. 2,940,847 to Kaprelian.

Although various electrode spacings may be employed, spacings of less than 1 mil and extending down even to the point where the electrodes are pressed together as in the case of the roller electrode constitute a particularly preferred form of the invention in that they produce better resolution and superior color separation results than is produced with wider spacings. This improvement is believed to take place because of the high field strength across the suspension during imaging.

In a monochromatic system, particles of a single color are dispersed in the carrier liquid and exposed to a black-and-white image. A single color image results, corresponding to black-and-white photography. In a polychromatic system, the particles are selected so that those of different colors respond to different wavelengths in the visible spectrum corresponding to their principal absorption bands. Also, the pigments should be selected so that their spectral response curves do not have substantial overlap, thus allowing for color separation and subtractive multi-color image formation. In a typical subtractive multi-color system, the particle dispersion should include cyan colored particles sensitive mainly to red light, magenta particles sensitive mainly to green light and yellow particles sensitive mainly to blue light. When mixed together in a carrier liquid, these particles produce a black appearing liquid. When one or more of the particles are caused to migrate from the injecting electrode towards the blocking electrode, they leave behind particles which produce a color equivalent to the color of the impinging light. Thus, for example, red light exposure causes the cyan colored particles to migrate, leaving behind the magenta and yellow particles which combine to produce red in the final image. In the same manner, blue and green colors are reproduced by the removal of yellow and magenta respectively. When white light impinges upon the mix, all particles migrate, leaving behind the color of the white or transparent substrate. No exposure leaves behind all pigments which combine to produce a black image. This is an ideal technique of sub tractive color imaging in that the particles are not only each composed of a single component but, in addition, they perform the dual functions of final image colorant and photosensitive medium. Typical photosensitive pigments include those described in copending applications Ser. No. 473,607, filed July 21, 1965 abandoned in favor of CIP Ser. No. 737,689 filed June 17, 1968; Ser. No. 421,281, filed Dec. 28, 1964 now U.S. Pat. No. 3,447,922 and Ser. No. 445,240, filed Apr. 2, 1965 now U.S. Pat. No. 3,384,632.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples further point out details of the electrophoretic imaging process of the present invention. All parts and percentages are by weight unless otherwise indicated. The following examples may be considered to represent preferred embodiments of the imaging process of this invention.

In each of the examples below, the suspension including finely divided electrically photosensitive particles is made up by dispersing the pigments in finely divided form in an insulating carrier liquid so that the pigments constitute about 8 percent by weight of the mixture. Where cyan, magenta and yellow particles are used, the mixture may be referred to as a tri-mix. In each example, the imaging operation is carried out using an apparatus of the sort shown in the Figures with the imaging mix carried in a porous electrode. The injecting electrode is connected in series with a switch, a potential source and the core of the blocking electrode. Where a roller electrode is used, the roller is approximately 2% inches in diameter. In each case, the movable electrode is moved across the planar electrode at about 4 centimeters per second. Exposure is by means of a Kodachrome transparency, with light intensity of about 1,000 foot-candles as measured on the uncoated NESA glass surface. Unless otherwise indicated, the blocking electrode core is held at a negative potential of about 2,500 volts with respect to the injecting electrode.

EXAMPLE I A tri-mix is prepared by dispersing about 8 parts of a pigment mixture consisting of a cyan pigment, Monolite Fast Blue GS, the alpha form of metalfree phthalocyanine, available from E. I. du Pont de Nemours & Co.; a magenta pigment, Watchung Red B, C. I. No. 15 865 l-( 4'-methyl-5 '-chloroazobenzene-2 -sulfonic acid)-2-hydroxy-3-naphthoic acid, available from E. l. du Pont de Nemours & Co. and a yellow pigment, 8,13- dioxodinaphtho-(2,1-b;2 ',3 -d)-furan-6carbox-pmethoxy-anilide, prepared by the method described in copending application Ser. No. 421,377, filed Dec. 28, 1964. This pigment mixture is dispersed in about parts Sohio Odorless Solvent 3440, a kerosene fraction available from Standard Oil of Ohio. A piece of acetylated cotton cloth is saturated with this mixture. The cloth is then wrapped around a conductive blocking electrode core as shown in FIG. 2 of the drawing. The roller is then passed across the NESA electrode surface while a color original is projected on the NESA surface and the potential is applied between the electrodes. An image of good quality conforming to the original in natural color is formed on the NESA electrode surface. This image is transferred to a receiving sheet by the process described in copending application 542,050, filed Apr. 12, 1966. The blocking elctrode is then again passed across the NESA electrode five additional times with transfer of images between imaging cycles. While there is a gradual decrease in image density and saturation, about three successive images of staisfactory quality are obtained.

EXAMPLE II An imaging suspension is prepared as in Example I above. A blocking electrode structure of the sort shown in FIG. 3 of the drawing is prepared. The core consists of a metal mesh tube surrounded by a 6 millimeter layer of porous polyurethane. The imaging suspension is introduced into contact with the porous overlayer. The roller is rotated to saturate the porous layer with the imaging suspension. This blocking electrode device is then passed across the NESA electrode while a color image is projected on the NESA electrode and the potential is applied between the injecting electrode surface and the metal mesh core of the blocking electrode. As the blocking electrode assembly passes across the NESA electrode, small amounts of suspension are continuously added and small amounts of suspension are simultaneously removed as shown in FIG. 3. An image of good quality confonning to the original is obtained. This image is transferred to a receiving sheet and the image forming steps repeated. Again, a good image results. Ten additional image forming and transferring cycles are then performed. While there is slight fall-off in color balance in the image, all of the ten images are of satisfactory quality.

EXAMPLE III A tri-mix is prepared consisting of a cyan pigment, Cyan Blue GTNF, C. I. No. 74160, the beta form of copper phthalocyanine, available from Collway Colors, a magenta pigment, Naphthol Red B, C. I. No. 12355, 1 2-methoxy-5 -nitro-phenylazo 2-hydroxy-3 nitro-3-naphanilide, available from Collway Colors; and a yellow pigment, Algol Yellow GC, C. I. No. 67300, 1,2,5 ,6-di (C,C '-diphenyl )-thiazoleanthraquinone, available from General Dyestuffs. The carrier liquid for this suspension is Isopar-G, a long chain saturated aliphatic hydrocarbon available from Humble Oil Company of New Jersey. Images are formed using this suspension in an apparatus of the sort shown in FIG. 2. A piece of porous polyurethane mate rial is soaked in this suspension and then wrapped around the conductive blocking elecgrode core. This blocking electrode is then passed across the NESA surface while a color image is projected on the NESA surface and a potential is imposed betweeen the two electrodes. An image of good quality is left on the NESA surface. This image is transferred to a receiving sheet. The porous blocking electrode is brought into contact with a supply of the imaging suspension.'A metal roller is rotated against the porous surface of the blocking electrode squeezing out the previous suspension and allowing fresh suspension to saturate the blocking electrode surface. Ten additional images are formed with transfer of the image and replenishment of the imaging suspension after each image is formed. Each of the successive images is of good quality with slight fall-off in color balance towards the end of the succession of images.

EXAMPLE IV A uni-mix is prepared consisting of a single pigment, the x-form of metal-free phthalocyanine, prepared as described in copending application 505,723, filed Oct. 29, 1965. About 7 parts of this finely divided pigment is dispersed in about 100 parts Sohio Odorless Solvent 3440. A monochromatic image is formed using this pigment with apparatus as schematically shown in FIG. 5. A mil Mylar film is laid on the NESA surface forming a blocking electrode. The injecting electrode is in the form of a roller having a porous sintered brass surface and interior means for supplying the imaging suspension to the porous surface. The imaging suspension is fed into the core of the injecting electrode until the porous surface is saturated. The injecting electrode is then rolled across the Mylar film while a negative monochromatic image is projected onto the Mylar surface and a potential of about 2,000 volts is imposed between the two electrodes. A positive image of good quality is formed on the Mylar surface. The Mylar film is removed and replaced with a fresh sheet. The imaging steps are then repeated with ten additional pieces of Mylar film. The images are found to be of consistently good quality.

Although specific components and proportions have been described in the above examples, other materials, as listed above, may be used where suitable with suitable results. In addition, other materials may be added to the imaging suspension or either of the electrodes to synergize, enhance or otherwise modify their properties. For example, the porous electrode or the imaging suspension may have wetting agents added thereto if desired. I

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

I claim:

1. an electrophoretic imaging apparatus comprising:

a. a pair of electrodes one of which is at least partially transparent and the other of which is of generally cylindrical configuration and porous to permit the flow of electrophoretic ink from internal thereof;

b. means supporting said two electrodes in virtual contact with each other to create an imaging zone at the area of virtual contact therebetween;

c. means to impose an electric field between said electrodes at the imaging zone;

d. means to project a light image through said transparent electrode at the imaging zone whereby an imaging action of electrophoretic ink thereat may occur and;

e. vacuum means adjacent said 'porous electrode for removing electrophoretic ink from said porous electrode.

. An electrophoretic imaging apparatus comprising:

. a first electrode which is at least partially transparent;

b. a second electrode of generally cylindrical configuration and being porous to permit the flow of electrophoretic ink therethrough to external thereof;

c. means supporting said first and second electrodes 4 in virtual contact with each other to create an imaging zone at the area of virtual contact therebetween said second electrode being positioned above said first electrode for permitting electrophoretic ink to flow in the direction of gravity to said first electrode;

d. means to impose an electric field between said electrodes at the imaging zone;

e. means to project a light image through said first electrode at the imaging zone whereby an imaging action of electrophoretic ink thereat may occur and;

f. vacuum means adjacent said second electrode for removing electrophoretic ink from said porous electrode. 

2. An electrophoretic imaging apparatus comprising: a. a first electrode which is at least partially transparent; b. a second electrode of generally cylindrical configuration and being porous to permit the flow of electrophoretic ink therethrough to external thereof; c. means supporting said first and second electrodes in virtual contact with each other to create an imaging zone at the area of virtual contact therebetween said second electrode being positioned above said first electrode for permitting electrophoretic ink to flow in the direction of gravity to said first electrode; d. means to impose an electric field between said electrodes at the imaging zone; e. means to project a light image through said first electrode at the imaging zone whereby an imaging action of electrophoretic ink thereat may occur and; f. vacuum means adjacent said second electrode for removing electrophoretic ink from said porous electrode. 